A typical gas turbine engine exhaust nozzle assembly on a commercial aircraft includes an annular nozzle surrounding a generally conically-shaped center body to form between them an annular exhaust exit for the engine core exhaust stream. FIG. 1 illustrates the basic geometry of the exhaust nozzle assembly.
Of course, the materials that form the exhaust nozzle assembly must be able to withstand the high temperatures and other environmental conditions. As the combustion temperatures of modern turbine engines increase, the exhaust temperatures may also increase. At a certain point, there are few or no metallic materials that can withstand such a high temperature environment with a reasonable part thickness and weight and while maintaining the mechanical and other properties needed for the exhaust assembly. Thus, ceramic-based materials are increasingly being explored for exhaust components. Ceramic components can also be generally lower weight than equivalent metallic components.
One problem to overcome with a ceramic-based exhaust component is how to mechanically attach the component to the metallic structures of the engine. Ceramics in general have a much lower coefficient of thermal expansions than metals. In an exhaust system made up of ceramic components attached to metallic support structure, the metallic support structure will expand to a much greater degree than the ceramic components when the system reaches the elevated operating temperatures. Thus, the mechanical attachment must take into account the relative expansion and movement between the ceramic components and the metallic components.